LibCore: Put all classes in the Core namespace and remove the leading C

I've been wanting to do this for a long time. It's time we start being
consistent about how this stuff works.

The new convention is:

- "LibFoo" is a userspace library that provides the "Foo" namespace.

That's it :^) This was pretty tedious to convert and I didn't even
start on LibGUI yet. But it's coming up next.

Servers/TelnetServer/Client.cpp

@@ -36,11 +36,11 @@
 #include <stdio.h>
 #include <unistd.h>
 
-Client::Client(int id, RefPtr<CTCPSocket> socket, int ptm_fd)
+Client::Client(int id, RefPtr<Core::TCPSocket> socket, int ptm_fd)
     : m_id(id)
     , m_socket(move(socket))
     , m_ptm_fd(ptm_fd)
-    , m_ptm_notifier(CNotifier::construct(ptm_fd, CNotifier::Read))
+    , m_ptm_notifier(Core::Notifier::construct(ptm_fd, Core::Notifier::Read))
 {
     m_socket->on_ready_to_read = [this] { drain_socket(); };
     m_ptm_notifier->on_ready_to_read = [this] { drain_pty(); };

Servers/TelnetServer/Client.h

@@ -37,7 +37,7 @@
 
 class Client : public RefCounted<Client> {
 public:
-    static NonnullRefPtr<Client> create(int id, RefPtr<CTCPSocket> socket, int ptm_fd)
+    static NonnullRefPtr<Client> create(int id, RefPtr<Core::TCPSocket> socket, int ptm_fd)
     {
         return adopt(*new Client(id, move(socket), ptm_fd));
     }
@@ -45,7 +45,7 @@ public:
     Function<void()> on_exit;
 
 protected:
-    Client(int id, RefPtr<CTCPSocket> socket, int ptm_fd);
+    Client(int id, RefPtr<Core::TCPSocket> socket, int ptm_fd);
 
     void drain_socket();
     void drain_pty();
@@ -61,9 +61,9 @@ private:
     // client id
     int m_id { 0 };
     // client resources
-    RefPtr<CTCPSocket> m_socket;
+    RefPtr<Core::TCPSocket> m_socket;
     Parser m_parser;
     // pty resources
     int m_ptm_fd { -1 };
-    RefPtr<CNotifier> m_ptm_notifier;
+    RefPtr<Core::Notifier> m_ptm_notifier;
 };

Servers/TelnetServer/main.cpp

@@ -106,8 +106,8 @@ static void run_command(int ptm_fd, String command)
 
 int main(int argc, char** argv)
 {
-    CEventLoop event_loop;
-    auto server = CTCPServer::construct();
+    Core::EventLoop event_loop;
+    auto server = Core::TCPServer::construct();
 
     int opt;
     u16 port = 23;